https://bugs.kde.org/show_bug.cgi?id=369459
Bug ID: 369459
Summary: valgrind on arm64 violates the ARMv8 spec (ldxr/stxr)
Product: valgrind
Version: 3.12 SVN
Platform: Compiled Sources
OS: Linux
Status: UNCONFIRMED
Severity: critical
Priority: NOR
Component: vex
Assignee: jsew...@acm.org
Reporter: pins...@gcc.gnu.org
So on ARMv8, valgrind invokes undefined behavior with respect to ldxr/stxr.
This causes valgrind to hang on ThunderX machines.
here is the disassembly when I attach gdb to the valgrind process:
0x00000008034001a4: ldxr w2, [x4]
0x00000008034001a8: mov x22, x2
0x00000008034001ac: and x24, x23, #0xffffffff
0x00000008034001b0: and x23, x22, #0xffffffff
0x00000008034001b4: str x24, [x21,#928]
0x00000008034001b8: str x23, [x21,#32]
0x00000008034001bc: dsb sy
=> 0x00000008034001c0: dmb sy
0x00000008034001c4: isb
….
0x00000008034000e4: stxr w0, w2, [x4]
As you can see there are plenty of stores and even DSB/DMB/ISB inbetween the
ldxr and stxr. All of this violates the ARM spec and says stxr can always fail
and it does on ThunderX.
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